The long-term goals of this research project are to understand the mechanisms that underlie speech perception by cochlear implant (CI) users, the characteristics of auditory perceptual learning in adults, and the potential links between the two. The first specific aim of the proposed research is to develop mathematical models of phoneme and word identification for individual Cl users. We will refine and extend our models of speech perception by CI users, which are based on the users' discrimination along specified perceptual dimensions. These psychophysically-based models are explanatory:, they do not simply attempt to predict overall scores in speech perception tests, they also provide specific hypotheses about the mechanisms CI users employ to process the auditory signal to identify different speech sounds. The second specific aim of this proposal is to investigate auditory adaptation in postlingually deaf Cl users, who receive speech signals that are both spectrally degraded and shifted in frequency. We will measure the extent, time course, and possible limitations of the adaptation shown by CI users. In addition to its strong clinical interest, this specific aim is scientifically important because the CI population presents a unique opportunity to investigate adaptation to a modified frequency map, and may allow us to obtain new knowledge about central auditory system plasticity in adults. The mathematical models developed in Project I will provide one of the methods to estimate a CI user's adaptation to a mismatched frequency map. The third specific aim is to test a gradual training approach that may facilitate auditory adaptation in postlingually deaf Cl users. The gradual and standard approaches to frequency mapping in Crs will be compared using a prospective randomized double-blind trial. We will examine both CI users and normal hearing listeners; the latter will be studied while hearing an acoustic model of a CI and will participate in imaging sessions that will search for functional neurobiological correlates of the auditory learning process. If successful, this study would be an example of translational research where basic knowledge about perceptual learning and adaptation in CI users is used to design improved clinical procedures. The proposed research program spans the range from basic to clinical to applied. Insights gained from this program will advance our basic knowledge about speech perception and adaptation to changes in the peripheral frequency map, and may also result in potentially important clinical applications. [unreadable] [unreadable]